Preconceptual thyroid peroxidase antibody positivity in women with recurrent pregnancy losses may contribute to an increased risk for another miscarriage

Abstract Objective To investigate preconceptual thyroid peroxidase antibody (TPO‐ab) positivity and/or thyroid stimulating hormone (TSH) levels in the upper range of normal as risk factors for recurrent unexplained first‐trimester miscarriage. Design A post‐hoc study of a randomized trial, in which acetylsalicylic acid did not affect the risk of a new miscarriage. Patients Women ( n = 483) with at least three unexplained recurrent first‐trimester miscarriages investigated at a Swedish secondary referral center. Measurements The levels of TPO‐ab and TSH were determined before pregnancy. The occurrence of a new first‐trimester miscarriage was analyzed by logistic regression with adjustments when applicable, for age, number of previous miscarriages, obesity and the investigated covariates levels of TPO‐ab and TSH. Results Including all first trimester miscarriages, odds ratio (OR) according to presence of TPO‐ab was 1.60 (95% confidence interval [CI]; 0.99–2.57), after adjustment 1.54 (95% CI; 0.94–2.53). Very early (biochemical) pregnancy losses occurred more often in women with than without preconceptual TPO‐ab (6.8% vs. 2.0%), OR 3.51 (95% CI; 1.15–10.71), after adjustment 2.91 (95% CI; 0.91–9.29). There was no association between TSH in the upper range of normal and a new miscarriage, adjusted OR 0.76 (95% CI; 0.32–1.83). A prediction model for a new miscarriage included number of previous miscarriages, woman's age and presence of TPO‐ab. Conclusion In women with at least three recurrent unexplained pregnancy losses, the presence of TPO‐ab may contribute to an increased risk of a first‐trimester miscarriage, possibly more pronounced in very early pregnancy. TSH levels 2.5–4.0 mU/L do not seem to increase the miscarriage risk.